Probing by time-resolved FTIR spectroscopy mass transport, molecular interactions, and conformational ordering in the system chloroform-syndiotactic polystyrene

The transport of chloroform in films of semicrystalline syndiotactic polystyrene (s-PS) in its nanoporous form (delta-form) has been investigated by gravimetric analysis and time-resolved FTIR spectroscopy. Experimental tests have been performed at 56 degreesC and at several vapor pressures ranging from 5 to 100 Torr. Sorption and desorption kinetics have been monitored with both techniques, and the dependence of diffusion coefficients with penetrant concentration was investigated, evidencing Fickian features typical of systems characterized by diffusivity increasing with concentration. Analysis of the vibrational spectrum of chloroform sorbed in the crystalline phase showed significant perturbations when compared to the spectrum of the isolated molecule or the molecule absorbed in amorphous s-PS. This perturbation has been attributed to host-guest molecular interactions whose strength was found to be relatively small. Conformational rearrangements of macromolecular chains in the amorphous phase were detected as a consequence of chloroform sorption. These rearrangements, which lead to an increase of the overall crystallinity degree, were quantified using the concept of critical sequence length (CSL). The kinetics of the conformational ordering process was found to parallel the sorption kinetics, and the associated increase of crystallinity was not reversible upon chloroform desorption.